Alternating-current motor.



PATENTED APR, 2,1907.'

Nox 848.1719

E. BRETGH.

ALTERNATING .CURRENT MOTOR.

APILIUATION FILED NOV.17, 1905.

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PATENTED APR. 2, 1907.

. BRETCH.

ALTERNATING CURRENT MOTOR. L

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inventori APPLICATION FILED NOV. 1'7, 1905.

Edwrd Brehch Aht'y's.

Uv b To all whom t may concern/:

, armature being preferably connected rarnnr Irrsinn.

EDWARD. BRETcIi, or Sr. LoUIS, MISSOURI.

- ALTEHNATINe-ouaasnr ino-ron.

Specification of Letters Patent.

Patented April 2, 1907.

I Application iiled November 17, `1905. Serial No. 287,803.

Be it known that l, EDWARD Bnn'rcn, citizen'of the United States, residing at St. Louis, Missouri, have invented a Icertain new and useful improvement in Alternating- Current'Motors, of which the following is a full, clear, and eXact description,"such as will enable others skilled in the art to which it appertains to make anduse the same, reference beinghad to the accompanying drawings, for/ming part of this speciiication, in whic Figure 1 isl an end view, partly broken away, of a motor embodying the features 'of my invention. Fig, 2 is a longitudinal sectional view of the motor shown in Fig. 1. Fig. 3 is a'` detail viewof one of the sections 'of the iield-core and one ofthe sections of the armature-core. 'Figs 4, V5, and 6 illustrate my improved armature usedlin motors having, respectively, a series-connection, a repulsion or inductionconnection, and a threephase circuit; and'.Fig. 7 is a' detail vview showing a modified form of my invention.

This invention relates to dynamo-electric machines for use on electric circuits wherein the current alternates, and particularly to the armatures used in such machines.

Theobect of 'my invention is to provide a machine` in which the armature is of very simple construction. and when employed in motors can-bef'startedunder load without the use,of .complicated mechanism and with a minimum startingcu'rrent.v

Another object is to provide a novel armature which will eliminate sparking at the cominutator'without the use of power-consuming res'istanc'es, diyided' windings, and similar devices which it has been necessary heretofore to use 'for' this purpose. y

Other desired. features "of my invention will be hereinafter pointed out.

I have shown theprefe'rred form of -invention as embodied. in an armature provided with two low-resistance windings separate and distinct from -each other. Preferably said armaturel isfused in combination with a laminated. .field-core having a number` of polar projections, lwhich may be wound in any ,well-known manner`common .to alternatingcurrent machines, one winding of the t0 commutator cooperating with brushes; The connections between the armatureand iield may be in anyof 'the well-l'rnowny ways, or; if

desired, the brushes may be short-circuited.

`ln the embodiment ofmy invention herein shown the armature is made up of a plurality of slotted laminations of magnetic material, and the slots in said sections receive an outer winding, which is similar and is connected to thecommutator as in direct-cur- .rentv armatures, and `an inner winding of the squirrel-cage typeof low resistance embedded.

in said core and separated s omedistance from the outer winding. i

Referring to the drawings, which represent a device embodying the preferred form of my invention, 2 designates a frame havin revolubly mounted therein an armature-s aft 4, carrying an armature-core 6 and a commutator 8, connected to a winding on the armature. A field-core 10 is mounted in a frame surrounding the armature, andthe commutator cooperates with pivotally-mounted brushes 12. As shown in the drawings, the iield-core is composed of a plurality of slotted laminations of magnetic material provided with a winding of well-known type. One of the slotted lamination's of the armature' is shown in detail in Fig.v 3. Extending trans.- `versely through openings in the laminations comprising the armature-core are a plurality of barsV 164 of lowresistance, preferably of copper or brass, and connected tothe opposite ends of saidba'rs are disks or plates 18, formed' of copper or brass and constituting a s uirrel-cage inner winding separated some distance from the outer .windingto forma path for the magnetic flux between the two windings. These bars, as here shown, are circular in cross-section; but in many cases it is advisable to use bars of oblong or rectangular cross-section in radialv Slots to provide a maximum cross-section of conductor in the squirrel-cage with the least reduction of the cross-section of the magnetic core.

In Fig. 4 I have shown my novel form of armature as embodied in a motor having a series connection, in Fig. 5 having a'repulsion or induction connection, and in Fig. 6 as vconnected for a three-phase circuit. In va similar manner a connection can be made for a two-phase circuit. The best torque characteristic for starting heavy loads is that of the series direct-current motor. Polyphase .induction-motors with short-circuitd armatures do not possess this characteristic; but for some classes of work their torque characteristic has proved'. satisfactory. Singlephase motors of this type have no starting 'torque' at all 'unless provided with. some IIO phase-splitting device, and then it is small and the starting-current exceedingly large, and to start heavy loads automatic clutchpulleys which throw the load on the motr after it has attained Aits speed must be used. This is generally accomplished by some device either manually or centrifugally operated to disconnect the phase-splitting device at running speed. These devices besides being expensive are a greatsource of trouble and are likely to burn out if for any reason the motor cannot start promptly. Another method which "utilizes the series starting characteristic employs a commutator on the As previously pointed out, a motor having.

the series characteristic above referred to had to be provided with expensive and complicated centrifugal devices to short-circuit the armature at the proper speed. My novel armature accomplishes the same result without the use of such devices, as at standstill or slow speed the magnetic flux in the armature, due to its high rate of alternations, will be forced outside the squirrel-cage winding in the path between said winding and the outer winding, so that the squirrel-cage winding will be inoperative. At or near'synchronous speed, however, the magnetic iux, due to its low rate of alternations in the armature, will penetrate the squirrel-cage winding, and thus cause it to become operative automatically, thereby producing the characteristics of a short-circuited winding Furthermore, the speed at which the short-circuited characteristie manifests itself depends on the lslip and not on the absolute speed, as in centrifugally-controlled devices, so that a Wide range of alternations in the supply-circuit is per-l mitted. In a motor employing a centrifugal device said device must be carefully adjusted and the frequency of the circuit held close to that fo'r which it is adjusted or it will fail. In my armature the squirrel-cage winding not only eliminates sparking and gives the shortcircuited characteristic at runnin speed, but also Amakes the armature more e fective, so thatheavier loads can be carried,

lallows the short-circuited characteristic to manifest itself at the proper speed irrespecti`ve of the absolute speed, and to come on gradually7 so that any shock or disturbance on the line is avoided.

Another advantage of my invention is thatV the speed of the motor can be'controlled by a suitable resistance or the startingcurrent held down to full-load current in the same y manner as in a'direct-current motor. Alternating-current motors with shrt-circuited armatures are not satisfactory as variablespeed motors, and onsingle-phase current they will not operate except near synchronous speed. By the usey of my l armature single-phase motors may be operated -at any speed below synchronous speed by connecting a suitable rheostat in series with the motor or by shifting the brushes and varying the relationbetween the windingsthey can be operated atespeeuds above synchronism when it is desirable.

By connecting the armature and field in series'and with the Aproper windings on the field and armature the power factor may be made very much higher than With the shortcircuited armature; but for motors of small size. in order to--secure the greatest simplicity I prefer to short-circuit the brushes and run as a repulsion-motor. In this manner only low voltages are applied` to the revolving armature, making insulation' extremely simple, and an armature will work equally Well in fields Wound for different voltages. This arrangement is also a great improvement over an armature having some short-circuited coils in the slots with the armature-winding. Such coils are usually ofhigh resistance to/ prevent them from burning out at slowspeed, in which case they are of little advantageat running speed. If these coils are of loW resistance, the starting-current'becomes excessive and the starting torque reduced. Either arrangement is open to the same objection as phase-splitting devices-that if the motorl cannot start promptly the coils will burn out. Placing a squirrel-cage Winding on the surface of the armature-,core in connection with .the commutated winding while not so liable to burn out gives no better results.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is- 4 l. In a dynamo-electric machine, a magnetic field in combination with an armature having a core of magnetic material, an outer carried by said core, means for controlling and directing the flow of the current in said winding, an inner winding located Within the zone of the outer winding and separated therefrom dto form a pathway for the magnetic flux to pass through the outer Winding Without penetrating the inner Winding; substantially as described.

2. An armature comprising a core of magnetic material, a commutated Winding of low resistance located at the eriphery of said core, an inner'winding or ow resistance located within the zone of the commutated winding and separated therefrom to form a pathway for the magnetic flux to pass through SoA IIO

" the commutated Winding Without penetrating the inner Winding 1 substantially es denetic material, a.- eommutated Winding of 10W resistance located near the periphery of said core, e squirrel-cage winding embedded in the core the zone of thecommutated and sev arated therefrom to form a pthway fort e' magnetic viiux to pass through the commute/ted Winding 'Without' penetrating thefsqinrrel-cage Winding; substen-tially as described.

4. .An amaturehavmgjaelewed laminated core of magnetic Qrnater'iah e' pommut'elt'edi Winding carriedbyk thefsl'otted portion of's'id eo're, an inner windinglcon isti'ng of transversely-extendnglbars fof e nducting matef rialembedded in'l the l core the zone. of n the Ycommutatedv windingjand separated therefrom to fori'n"` ailathwa'y for vmagnetic flux to pass through t of said bars; substentiallyvas described.

scribedl v 'f In testimony signature, in the presence of two `r`this-7th day ofNovember, l1905;

- Witnesses e commutated Wind? Without penetrating the inner Winding, and conducting means connected to the ends rial, a commutatedwinding of 10W resistance carried by' said core, an inner Winding of 10W, 3o

resistance carried by said core andfflocate'd thezone of the commutated Winding 'A and 'separated therefrom to form a lpathway ,for rthe magnetic flux t'pass through the oonrmutated vsyrinding' Without enetrating v725 5. In a d nemo-electric machine, a slotted` fiammated `e1dcor`e in combination With en armature having a core of magneticmate' the inner IWinding; substantie y as defv whereof'I hereunto ax my witnesses, 

